Experts urge better detection and poultry production practices in response to a new mutant strain of H5N1 appearing in the northern and central parts of the country

Cooked chicken are displayed for sale on a street in Hanoi. The United Nations Food and Agriculture Organization warned against a new strain of H5N1 virus in Asia that is resistant to all available vaccines.

More hygienic practices have been urged for poultry farmers, traders and slaughterers in Vietnam after the United Nations warned against a mutant strain of the deadly bird flu virus in Asia.

"Control measures must focus on reducing the transmission of the virus both to other poultry and to man. These changes must be made on the farm, by traders and at markets/slaughterhouses level, but must be promoted by government," said John Weaver, Chief Technical Adviser of the United Nations' Food and Agriculture Organization (FAO) in Vietnam.

"Key transmission pathways for this virus are bird to bird spread, and through contaminated materials and equipment such as manure, feathers, vehicles and clothing," he told Thanh Nien Weekly.

The warning came after the FAO announced on Monday (August 29) a possible major resurgence of the H5N1 (highly pathogenic avian influenza or bird flu virus), amid signs that a mutant strain of the deadly bird flu virus is spreading in Asia and beyond.

The H5N1 virus has infected 565 people since it first appeared in 2003, killing 331 of them, according to the World Health Organization (WHO) figures. The latest death occurred earlier this month in Cambodia, which registered eight cases of human infection this year - all of them fatal.

So far, H5N1 has killed or forced the culling of more than 400 million domestic poultry and caused an estimated US$20 billion of economic damage across the globe before it was eliminated from most of the 63 countries infected at its peak in 2006, according to the FAO.

However, the virus remained endemic in six nations, although the number of outbreaks in domestic poultry and wild bird populations shrank steadily from an annual peak of 4,000 to just 302 in mid 2008. But outbreaks have risen progressively since, with almost 800 cases recorded in 2010-2011.

"The general departure from the progressive decline observed in 2004-2008 could mean that there will be a flare-up of H5N1 this fall and winter, with people unexpectedly finding the virus in their backyard," said FAO Chief Veterinary Officer Juan Lubroth.

No vaccine available

Lubroth said the appearance in China and Vietnam of a variant virus able to sidestep the defenses of existing vaccines prompted further concern.

Vietnam suspended its springtime poultry vaccination campaign this year. FAO said most of the northern and central parts of the country - where H5N1 is endemic - have been invaded by the new virus strain, known as H5N1 - 2.3.2.1.

The countries where H5N1 is still firmly entrenched Bangladesh, China, Egypt, India, Indonesia and Vietnam are likely to face the biggest problems, but no country can consider itself safe, warned Lubroth.

Weaver said current vaccines do not adequately protect against the new H5N1 strain as the antigenicity of this new virus has changed. "That is, the "˜face' of the virus has changed and is no longer recognized by the antibodies produced by the current vaccine," he said.

"This change of virus is an ongoing process with the influenza viruses and happens continually - often with little consequence. However, on this occasion, a virus with different antigenicity has evolved," he said.

According to Weaver, a new vaccine can be developed very quickly using modern molecular manipulation techniques, but testing and production of the vaccine takes some time.

"A new vaccine is not likely to become available until next year," he said.

No feasible immediate action

Weaver said the key lesson learned by Vietnam and other countries is that there is no "quick fix" solution to fighting bird flu and other major diseases.

"There is no simple panacea to reduce the threat this new virus strain poses. Control measures must focus on reducing the transmission of the virus both to other poultry and to man.

"The fundamental problem with bird flu in Vietnam is the lack of hygiene and biosecurity on farms, by traders and at markets and slaughterhouses. To reduce the risk of this disease there needs to be the long-term development of improved poultry production and marketing," he said.

He said the current poultry production systems in Vietnam will never manage to eradicate the disease despite disease detection, and response plays an important role in reducing the risk to people and poultry.

"Vietnam has had an active control program against H5N1 avian influenza since the disease was first detected in 2003. This control program has been successful and cases of H5N1 in poultry and people have declined dramatically. Notwithstanding this success, H5N1 has remained endemic in Vietnam with many provinces detecting infection every year."

Jan Slingenbergh, a senior animal health officer at FAO and head of FAO's Emergency Prevention System (EMPRES) for trans-boundary diseases, said intensive monitoring, genetic sequencing, and acquisition of adequate vaccine supplies would appear to be among the main priorities.

"Vietnam has not carried out a large scale, systematic spring vaccination scheme this year. However, there may be a need for a more significant, targeted scheme this fall, as based on actual risk findings," he told Thanh Nien Weekly.

"The fact that viruses evolve against the vaccines is in itself not unusual. China has the capability to respond with novel vaccines, mass produced mostly within a year. Viruses circulating in China may show up in Vietnam because of poultry trade," he said.

However, Slingenbergh is optimistic about Vietnam's actions against bird flu.

"Vietnam has received international praise for transparency, collaboration and taking a high level of initiative. Hopefully, this will continue," he said.

According to FAO, Vietnam's veterinary services are on high alert and considering a targeted vaccination campaign this fall.

The WHO meets twice a year, in February and September, when experts discuss and decide on the makeup of candidate influenza vaccines.

Virologists said the mutation of flu virus is not unusual and scientists have to keep changing the vaccine strains. So far, H5N1 kills up to 60 percent of the people it infects.